1. Field of the Invention
The invention relates to a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer, a semiconductor crystal substrate having a pair of facing surfaces and a semiconductor device comprising the semiconductor laminated substrate and the semiconductor crystal substrate and a method of manufacturing the same.
2. Description of the Related Art
A III-V nitride semiconductor composed of gallium nitride (GaN) or the like is a direct gap semiconductor having energy band ranges from 1.9 eV to 6.2 eV, and thus gallium nitride receives attention as a material for constituting an optical element ranging from a visible region to an ultraviolet region. Gallium nitride has about 2.5xc3x97107 cm/s by saturation rate and about 5xc3x97106 V/cm by breakdown electric field, which are higher than those of any other electronic material. Thus, gallium nitride is considered to have a great potential for the material for constituting an electron transit element for a high frequency and a large power.
However, it is extremely difficult to grow a bulk crystal from a melt because the III-V nitride semiconductor has a high melting point and also a vapor pressure of nitrogen is high near the melting point. Thus, the crystal of the III-V nitride semiconductor is generally obtained by epitaxial growth on a base substrate made of sapphire, silicon carbide, spinel, lithium gallate or the like. However, since such a base substrate has a different lattice constant from the III-V nitride semiconductor, a large amount of lattice defects occur in the crystal of the III-V nitride semiconductor grown on this base substrate.
Therefore, a method of reducing the defects by employing selective growth technology, for example, has been recently used (see Y. Kato, J. Crystal Growth, 144 (1994) 133). This method is, for example, that a mask layer having an opening and composed of silicon dioxide (SiO2), silicon nitride (Si3N4) or the like is formed on a thin film of the III-V nitride semiconductor grown on the base substrate and then the crystal of the III-V nitride semiconductor is grown through the opening of the mask layer. According to this method, the crystal is transversely grown through the opening of the mask layer, whereby the propagation of the through dislocation is blocked and thus the defects are reduced. This method applies the technology for growing the crystal of gallium arsenide (GaAs) on the substrate made of silicon (Si) and gets great effect on the crystal growth of the III-V nitride semiconductor.
However, although a reduction in the defects is thus attempted, the following problems exist when the base substrate made of sapphire or the like is used. In the case of the base substrate made of sapphire, the following problems occur. First, difficulty in cleavage makes it impossible for the cleavage to form an end surface for the exit of the light with excellent reproducibility for the preparation of a laser or the like. Second, two types of electrodes must be positioned from the same side due to insulating properties. Third, low thermal conductivity results in a temperature rise of an active layer in a light emitting device or a channel layer in the electron transit element, thereby causing deterioration of the device or element. In order to solve these problems, it is therefore preferable that the base substrate is used only for growing the crystal and then the base substrate is removed after the crystal is grown.
Methods of removing the base substrate include a mechanical lapping method and a chemical etching method, for example. The mechanical lapping method is not practical because lapping with-keeping a large area is difficult due to bowing of the base substrate grown the III-V nitride semiconductor. On the other hand, the chemical etching method is preferable because of no mechanical damage. For example, the method, in which the III-V nitride semiconductor is grown on the base substrate through a buffer layer composed of oxide such as zinc oxide (ZnO) or magnesium oxide (MgO) and then the buffer layer is removed by etching, is proposed as the method of isolating the base substrate by the etching (see Unexamined Japanese Patent Application Publication No. 7-165498, No. 10-178202 and No. 11-35397).
However, since in this method, the III-V nitride semiconductor is only grown through the buffer layer composed of oxide, the base substrate cannot be isolated for the following reasons. First, if the buffer layer composed of oxide is as thin as tens of nanometers, the buffer layer disappears at the time of the growth of the III-V nitride semiconductor and thus the presence of the buffer layer cannot be confirmed. Secondly, even if the buffer layer remains in the form of normal oxide, the III-V nitride semiconductor is precipitated on the sides on the periphery of the base substrate and thus the buffer layer is coated with the III-V nitride semiconductor. Consequently, an etchant cannot be brought into contact with the buffer layer and thus the buffer layer cannot be etched. Thirdly, even if the etchant is in contact with the buffer layer, an ordinary etching speed is about a few micrometers per minute and viscosity resulting from a dissolved component increases in accordance with the etching. Consequently, an enormous time is required to impregnate the etchant into near the center of the base substrate of 2 inches diameter, for example. In ID fact, the etching stops after reaching up to about hundreds of micrometers, and thus it is difficult to isolate the base substrate.
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide a semiconductor laminated substrate and a semiconductor device capable of easily isolating a base substrate by etching and a method of manufacturing the same, and a semiconductor crystal substrate and a semiconductor device obtained by the method and a method of manufacturing the same.
A semiconductor laminated substrate of the invention having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer comprises a flow-through hole for flowing therethrough an etchant for etching the separating layer.
A semiconductor crystal substrate of the invention having a pair of facing surfaces comprises projections or depressions on one of the facing surfaces.
In a semiconductor device of the invention comprising a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer, the semiconductor laminated substrate has a flow-through hole for flowing therethrough an etchant for etching the separating layer.
In another semiconductor device of the invention comprising a semiconductor crystal substrate having a pair of facing surfaces, the semiconductor crystal substrate has protrusions or depressions on one of the facing surfaces.
A method of manufacturing a semiconductor laminated substrate of the invention having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer comprises the step of forming a flow-through hole for flowing therethrough an etchant for etching the separating layer.
A method of manufacturing a semiconductor crystal substrate of the invention in a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer and having a flow-through hole for flowing therethrough an etchant for etching the separating layer comprises the step of etching the separating layer by flowing the etchant through the flow-through hole, thereby isolating the semiconductor crystal layer from the base substrate.
A method of manufacturing a semiconductor device of the invention uses a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer and having a flow-through hole for flowing therethrough an etchant for etching the separating layer.
Another method of manufacturing a semiconductor device of the invention using a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer and having a flow-through hole for flowing therethrough an etchant for etching the separating layer comprises the step of etching the separating layer by flowing the etchant through the flow-through hole, thereby isolating the base substrate.
Still another method of manufacturing a semiconductor device of the invention in a semiconductor laminated substrate having a base substrate and a semiconductor crystal layer formed on the base substrate sandwiching a separating layer and having a flow-through hole for flowing therethrough an etchant for etching the separating layer uses a semiconductor crystal substrate which is formed by etching the separating layer by flowing the etchant through the flow-through hole and thereby isolating the semiconductor crystal layer from the base substrate.
A further method of manufacturing a semiconductor device of the invention uses a semiconductor crystal substrate having a pair of facing surfaces, one of which has protrusions or depressions.
A semiconductor laminated substrate of the invention has the flow-through hole for flowing therethrough the etchant for etching the separating layer. Thus, the separating layer is easily removed by etching, and therefore the semiconductor crystal layer is easily isolated from the base substrate.
A semiconductor crystal substrate of the invention has the protrusions or the depressions on one of the facing surfaces.
A semiconductor device of the invention comprises the semiconductor laminated substrate of the invention or the semiconductor crystal substrate of the invention.
In a method of manufacturing the semiconductor laminated substrate of the invention, the flow-through hole for flowing therethrough the etchant for etching the separating layer is formed.
In a method of manufacturing the semiconductor crystal substrate of the invention, the separating layer is etched by flowing the etchant through the flow-through hole, whereby the semiconductor crystal layer is isolated from the base substrate.
In a method of manufacturing the semiconductor device of the invention, the semiconductor laminated substrate of the invention is used.
In another method of manufacturing the semiconductor device of the invention, the separating layer is etched by flowing the etchant through the flow-through hole, whereby the base substrate is isolated.
In still another method of manufacturing the semiconductor device of the invention in the semiconductor laminated substrate of the invention, the semiconductor crystal substrate formed by etching the separating layer by flowing the etchant through the flow-through hole and thereby isolating the semiconductor crystal layer from the base substrate, is used.
In a further method of manufacturing the semiconductor device of the invention, the semiconductor crystal substrate having a pair of facing surfaces, one of which has the protrusions or the depressions, is used.
Other and further objects, features and advantages of the invention will appear more fully from the following description.